The invention relates to percutaneously delivered stent grafts for repairing an abdominal aortic aneurysms.
An abdominal aortic aneurysm is a sac caused by an abnormal dilation of the wall of the aorta, a major artery of the body, as it passes through t he abdomen. The abdomen is that portion of the body which lies between the thorax and the pelvis. It contains a cavity, known as the abdominal cavity, separated by the diaphragm from the thoracic cavity and lined with a membrane, the peritoneum. The aorta is the main trunk, or artery, from which the systemic arterial system proceeds. It arises from the left ventricle of the heart, passes upward, bends over and passes down through the thorax and through the abdomen to about the level of the fourth lumbar vertebra, where it divides into the two common iliac arteries.
The aneurysm often arises in the infrarenal portion of the diseased aorta, for example, below the kidneys. When left untreated, the aneurysm will eventually cause rupture of the sac with ensuing fatal hemorrhaging in a very short time. High mortality associated with the rupture has led to the present state of the art and the trans-abdominal surgical repair of abdominal aortic aneurysms. Surgery involving the abdominal wall, however, is a major undertaking with associated high risks. There is considerable mortality and morbidity associated with this magnitude of surgical intervention, which in essence involves replacing the diseased and aneurysmal segment of blood vessel with a prosthetic device which typically is a synthetic tube, or graft, usually fabricated of either DACRON(copyright), TEFLON(copyright), GORTEX(copyright), or other suitable material.
To perform the surgical procedure requires exposure of the aorta through an abdominal incision, which can extend from the rib cage to the pubis. The aorta must be cross-clamped both above and below the aneurysm, so that the aneurysm can then be opened and the thrombus, or blood clot, and arterioscleriotic debris removed. Small arterial branches from the back wall of the aorta are tied off. The DACRON(copyright) tube, or graft, of approximately the same size of the normal aorta is sutured in place, thereby replacing the aneurysm. Blood flow is then reestablished through the graft. It is necessary to move the intestines in order to get to the back wall of the abdomen prior to clamping off the aorta.
If the surgery is performed prior to rupturing of the abdominal aortic aneurysm, the survival rate of treated patients is markedly higher than if the surgery is performed after the aneurysm ruptures, although the mortality rate is still relatively high. Although abdominal aortic aneurysms can be detected from routine examinations, the patient may not experience any pain from the condition. Thus, if the patient is not receiving routine examinations, it is possible that the aneurysm will progress to the rupture stage.
Disadvantages associated with the conventional, prior art surgery, in addition to the high mortality rate, are: the extended recovery period associated with the large surgical exposure in such open procedures; difficulties in suturing the graft, or tube, to the aorta; the loss of the existing thrombosis to support and reinforce the graft; the unsuitability of the surgery for many patients having abdominal aortic aneurysms; and the problems associated with performing the surgery on an emergency basis after the aneurysm has ruptured. As to the extent of recovery, a patient can expect to spend from 1 to 2 weeks in the hospital after the surgery, a major portion of which is spent in the intensive care unit, and a convalescence period at home from 2 to 3 months, particularly if the patient has other illness such as heart, lung, liver, and/or kidney disease, in which case the hospital stay is also lengthened. Since the graft must be secured, or sutured, to the remaining portion of the aorta, it is often difficult to perform the suturing step because of thrombosis present on the remaining portion of the aorta, and that remaining portion of the aorta wall may be friable, or easily crumbled.
Since the thrombosis is totally removed in the prior art surgery, the new graft does not have the benefit of the previously existing thrombosis therein, which could be utilized to support and reinforce the graft, were the graft to be able to be inserted within the existing thrombosis. Since many patients having abdominal aortic aneurysms have other chronic illnesses, such as heart, lung, liver, and/or kidney disease, coupled with the fact that many of these patients are older, these patients are not ideal candidates for such surgery, which is considered major surgery. Such patients have difficulties in surviving the operation. Lastly, once the aneurysm has ruptured, it is difficult to perform a conventional surgery on an expedited basis because of the extent of the surgery.
Accordingly, the prior art teaches various methods and apparatuses for repairing an abdominal aortic aneurysm which is believed to lower morbidity and mortality rate by not requiring an abdominal incision and general anesthesia, not requiring suturing the graft to the remaining aortic wall, and which permits the existing aortic wall and thrombosis therein to be retained to reinforce and support the aortic graft. An example of such a method and apparatus is given in U.S. Pat. Nos. 5,316,023 issued to Palmaz et al. on May 31, 1994; 5,360,443 issued to Barone et al. on Nov. 1, 1994; 5,578,071 issued to Parodi on Nov. 26, 1996; and 5,591,229 issued to Parodi on Jan. 7, 1997, all of which are hereby incorporated herein by reference.
Devices, such as the one shown in the above referenced Barone patent, use an improved method for repairing an abdominal aortic aneurysm in an aorta having two iliac arteries associated therewith. The device includes first and second tubes, preferably made from a variety of materials such as DACRON(copyright) and other polyester materials, TEFLON(copyright) (polytetrafluoroethylene), TEFLON(copyright) coated DACRON(copyright), porous polyurethane,silicone, expanded polytetrafluoroethylene, and expanded polyurethane. It is preferred that all of the foregoing materials be porous to allow for an intimal layer to form on the tubes. Each of the tubes are connected to expandable and deformable tubular members, or stents. These stents can be similar in structure to those described in disclosed in U.S. Pat. Nos. 4,733,665 issued on Mar. 29, 1988; 4,739,762, issued on Apr. 26, 1988; and 4,776,337 issued on Oct. 11, 1988, all of the foregoing patents being in the name of Julio C. Palmaz, each of which is incorporated herein by reference. Each of the tube/stent structures are then disposed on the end of a balloon catheter. Either both tubes are inserted into the same femoral artery or one of the tubes is inserted into one femoral artery of the patient and the other tube is inserted into the other femoral artery of the patient. Thereafter the tubes are intraluminally delivered to the aorta, thereby disposing at least a portion of each tube within the abdominal aortic aneurysm. The balloons on the distal ends of the catheters are then expanded to expand and deform the tubular members, to force the tubular members radially outwardly into contact with the aorta and each other. This secures the tubular members and a least a portion of each tube within the aorta, whereby the tubes provide a bilateral fluid passageway through the abdominal aortic aneurysm.
While the above mentioned devices would seem to work well, there is a desire to improve upon the device. More particularly, there was a need to ensure that most of the blood flowing through the abdomen flows through the bilateral fluid passageways and not around them where it could cause further damage. The precursor stent gasket described in commonly assigned European Patent Application EP 0947179, filed on Mar. 29, 1999, European Patent Application EP 1000590 (A1), filed on Nov. 8, 1999, and pending U.S. patent application Ser. No. 09/404,660 filed on Sep. 24, 1999, the disclosures of which are hereby incorporated herein by reference, limits the amount of blood which could leak around the bilateral fluid passageways and into the aneurysm. The precursor stent gasket is positioned within the infrarenal neck, between an abdominal aortic aneurysm and the renal arteries, of a patient to assist in repairing the abdominal aortic aneurysm. The stent is designed to be coupled to the bilateral grafts for directing blood flow. The graft has a distal end for positioning distal to the aneurysm, and a proximal end for positioning proximal to the aneurysm. The precursor stent gasket includes a substantially cylindrical expandable member having a proximal end, a distal end and an interior. The stent gasket further includes a compressible gasket member located within the interior of the expandable member and attached thereto. The compressible member is substantially impervious to blood when in a compressed state and is coupled the graft. This is so the coupled device can direct blood flow through the graft, with the gasket member substantially preventing blood from flowing into the aneurysm.
While the above described devices are large improvements over the prior art, there has been a need for improvement. There has been a desire to have a better device for attaching the graft material to the grafts used in the above described devices. There has been a desire to have an improved stent gasket member for better attachment of the stent gasket member to aortic wall. There has been a desire to have a mechanism for ensuring that the stent gasket member is not prematurely deployed. There has been a desire to improve the design of the stent grafts to make them perform better. Lastly, there has been a desire to improve the grafts on the stent grafts themselves to make them perform better during deployment. The following described invention provides such an improved device.
In accordance with the present invention there is provided an improved stent graft for insertion into a body vessel of a patient. The stent graft includes a hollow substantially cylindrical stent comprising a plurality of interconnected struts. In addition, the stent graft includes a graft material attached to the stent, wherein the graft material is an open cell foam material having a multiplicity of cells having an average diameter ranging from about 100-500 micrometers, and a cell density on a surface thereof ranging from about 50-100 cells per inch.